1. Technical Field
The preset invention relates to a robot for arc welding.
2. Description of the Related Art
In an arc welding robot in recent years, a tube or wire required for welding is usually contained in a robot arm together with a control cable for a driving servomotor of the robot. However, since a welding wire is inserted in a welding wire conduit for connecting a wire feeding device and a wire supplying source, the conduit does not have flexibility. Further, since periodical maintenance is required to the conduit, it is difficult to contain the conduit in a narrow space of the robot arm. Therefore, in a conventional welding robot, it is necessary to arrange the conduit along the robot arm and fix some points of the conduit to the robot arm, so that the conduit may follow the motion of the robot arm. Such arrangement and fixing of the conduit is troublesome.
In recent years, a flexible welding wire conduit has been developed. Also, a technique has been developed, in which a robot having a robot arm is mounted on a pedestal, and a wire conduit is arranged along the robot arm and then is inserted in a hollow portion of a rotating part of the robot. For example, Japanese Unexamined Patent Publication No. 8-155881 discloses an industrial robot having a guide tube extending from a lower face of a base through an upper frame of a rotating part of the robot, and a hose or the like inserted into the guide tube, which feeds a welding core fiber to a processing tool.
In a conventional configuration, in the motion range required for an upper arm of the robot, for example, the upper arm is rotated toward the front side of the robot by 160 degrees or rotated toward the rear side of the robot by 90 degrees when the upper arm vertically extends relative to the install surface of the robot is set as a reference position (or orientation), the bend radius of the conduit for the welding wire may become smaller, whereby the welding wire within the conduit is strongly compressed against the inner surface of the conduit and the welding wire cannot be smoothly fed in the conduit. Since the welding wire is continuously fed in the conduit during welding operation, when the welding wire is strongly compressed against the conduit, the inner surface of the conduit may be damaged, in addition that the welding wire is not stably fed. Further, in the case that the robot has a forearm connected to the upper arm, when the forearm is folded forward or backward relative to the upper arm, the bend radius of the welding wire becomes smaller, whereby a problem similar to the above may occur.
Even when the welding wire is normally fed in the conduit, since powder generated by abrasion is in the wire conduit, it is necessary to periodically clean the inside of the conduit or replace the conduit. In order to pull-out the conduit from the hollow portion of the rotating body of the robot and return the conduit after cleaning or insert a new conduit to the hollow portion, it takes more time than if the conduit is arranged along the outside of the robot. In other words, when the conduit is inserted in the hollow portion of the rotating body, it is necessary to pull-out the conduit from the pedestal side near the install surface of the robot and then insert the conduit into a generally narrow hollow portion, which is troublesome.